The bad old days return to the South Street Seaport:

A mystery odor wafting through the seaport’s residential neighborhood for the past few weeks has restaurants reeling, homeowners gagging and tourists left holding their noses.

“It’s disgusting — like rotten fish left out on a sidewalk for a year,” said Venanzio Pasubio, 33, owner of ll Brigante, a restaurant on Front Street.

With the Fulton Fish Market long gone, theories abound on the origin of the odor. Some think it’s illegal dumping; others point fingers at the Waterfalls art project; one person insists that it’s the preserved corpses on display at “Bodies, the Exhibition” nearby.

. . .

Locals describe the smell as “dead rat,” “stinky cheese” and “raw sewage.”

“We’re supposed to be up and coming and trendy,” said resident Ellen Murphy. “Now we just smell like fish.”

The Post brought in smell scientist Dr. Avery Gilbert, author of “What the Nose Knows,” to investigate.

“Yes that is fish,” he said about the elusive smell. “But it’s also yeasty, like bread.”

He said the culprit is most likely “amines,” which is the fish-like smell of “proteins breaking down.”

Location Scout: South Street Seaport.